Google is in the process of shutting a number of products which haven't had the impact the company hjoped for, including the ambitious project to make renewable energy cheaper than coal.

Google's "Renewable Energy Cheaper than Coal (REpublished results to help others in the field continue to advance the state of power tower technology, and has closed its efforts.

"We will continue our work to generate cleaner, more efficient energy - including our on-campus efforts, procuring renewable energy for our data centers, making our data centers even more efficient and investing more than $850 million in renewable energy technologies," Urs Holzle, Senior Vice President, Operations & Google Fellow wrote in a blog post.

Google also announced additional plans part of its so-called "spring cleaning" announcement that Google has made since Google co-founder Page took the reins in April.

Specifically, on December 19, Google plans to quit Google Bookmarks Lists - an experimental feature for sharing bookmarks and collaborating with friends. All bookmarks within Lists will be retained and labeled for easier identification, while the rest of Google Bookmarks will function as usual, Google said.

Google Friend Connect, which allows webmasters to add social features to their sites by embedding a few snippets of code will be also retired for all non-Blogger sites on March 1, 2012. Google encourages affected sites to create a Google+ page and place a Google+ badge on their site.

Google Gears browser extension for creating offline web applications has stopped supporting new browsers since March. On December 1, 2011, Gears-based Gmail and Calendar offline will stop working across all browsers, and later in December Gears will no longer be available for download. This is part of Google's effort to help incorporate offline capabilities into HTML5.

Google Search Timeline is also left in the dust since users are able to restrict any search to particular time periods using the refinement tools on the left-hand side of Google's search page. Additionally, users who wish to see graphs with historical trends for a web search can use google.com/trends or google.com/insights/search/ for data since 2004.

As of January 31, 2012, Google Wave will also become read-only and users won't be able to create new ones. On April 30 the service will be completely turned off.

Gogle launched Knol in 2007 to help improve web content by enabling experts to collaborate on in-depth articles. Google says that Knol will work as usual until April 30, 2012, and users can download their knols to a file and/or migrate them to WordPress.com. From May 1 through October 1, 2012, knols will no longer be viewable, but can be downloaded and exported. After that time, Knol content will no longer be accessible.